1. Field of the Invention
The present invention relates to dental dispensing cups and, more particularly, to cups for simultaneously dispensing the base and catalyst pastes of addition cured vinyl silicones used in making dental impressions.
2. Description of the Related Art
Addition cured vinyl silicone materials such as polyvinylsiloxane elastomers are widely used in dentistry because they can provide highly accurate impressions, are simple to prepare and apply, and are available in a range of viscosities to accommodate different impression techniques. Typically, two paste admixtures having a putty-like consistency, a base portion and a catalyst portion, are constituted so that prior to their being combined one component needed for polymerization is missing in each portion. U.S. Pat. No. 4,806,575 (Waller et al., 1989) discloses suitable compositional ranges for components of base and catalyst portions combined in a 1-to-1 ratio. The base paste composition consists of, by weight: a vinyl-substituted long chain silicone, vinyl polydimethylsiloxane (10-60%); a hydrogen-substituted polysiloxane, hydropolydimethyl siloxane (1-10%), which acts as a cross-linking actuator only in the presence of a catalyst; a silica filler (20-80%); and liquid petroleum (0-15%). The catalyst paste composition consists of, by weight: vinyl polydimethylsiloxane (10-60%); cyclic vinyl siloxane (0-1%); chloroplatinic acid catalyst complex (0.1-5.0%); plasticizer (0-15%); filler (20-80%); and extremely finely divided platinum black (0.1-10,000 ppm). When the two pastes are combined, the platinum in the chloroplatinic acid activates the hydropolydimethyl siloxane which actuates cross-linking polymerization of the vinyl polydimethylsiloxane. Noticeable cross-linking (end of "working time") proceeds over a short time to almost total cross-linking ("setting time") of the resultant elastomeric silicone gum.
Because making an impression requires loading a fairly precise amount of the elastomeric material onto a dental tray, it is convenient to have available premeasured amounts of the base and catalyst portions in a single two-compartment dispensing package. However, juxtaposing or otherwise disposing these two admixtures in close proximity risks leakage of the catalyst into the compartment containing the cross-linking actuator or leakage of the actuator into the compartment containing the catalyst, particularly when a package is stored rather than being used soon after arriving in the dental office. The present invention overcomes this problem.
Dental dispensing cups are known in the art. U.S. Pat. No. 4,844,308 (Porteous, 1989) and U.S. Pat. No. 4,717,057 (Porteous, 1988) disclose a disposable sealed cup having an open mouth defined by a rim, filled with a dispensable material such as dental paste. The cup includes a removable closure overlying the open mouth and a ring-like finger mount extending from the rim. U.S. Pat. No. 3,327,391 (Malm, 1967) discloses a disposable, clear acetate, dental material cup containing dental medicaments or pumices and provided with a cellophane cover that may be heat sealed to the outwardly projecting rim of the cup. The cup bottom is provided with a projection adapted to be slip-fitted or snap-connected to a supporting non-disposable finger ring. U.S. Pat. No. 2,970,379 (Hardgrove, 1961) discloses a sterilizable, vertically disposed and pivotally connected, two-compartment, finger supportable dental tray for holding plastic filling materials, dental cleaning compounds or medications. The upper compartment forms a closure for the lower compartment, and the lower compartment is provided with a lateral rim from which extends a finger-engageable ring-like member.
Methods for configuring thermoplastic sheet into single- and multi-compartment packages, dispensing cups and similar articles also are known. For example, thermoformed dual-compartment packages having a sealed, removable closure are commonly used for cupcakes and other pastries. Specific to the dental arts, U.S. Pat. No. 5,009,056 (Porteous, 1991) discloses a method for preparing a substantially fluid impervious, sealed, dental paste dispensing cup having an integrated finger mount. Thermoplastic sheet is converted into a plurality of cup configurations by subjecting the sheet to the operations of a multi-cavity thermoforming machine, commonly called a vacuum former, wherein the sheet is heated to a pliable, plastic state and forced by a vacuum or other technique against the contours of each cavity. Upon cooling, the plastic retains the shape and details of the cavity. Various aspects of thermoforming, including sheet materials, machines, molds, thermoforming techniques, thermoforming variables and finishing are extensively considered in the following reference: W. K. McConnell Jr., Thermoforming, Modern Plastic Encyclopedia, Vol. 45, No. 14a, pp. 776-792, McGraw-Hill, 1968-1969.
One thermoforming method for producing cup-shaped "deep-draw"-formed articles from a plastic sheet is the plug-assist pressure method. First, a heated and softened sheet is forced into a female mold by a short-nosed plug. Then pressured air is introduced between the plug and sheet to allow the sheet to come into full contact with the mold. The sheet is then cooled to obtain the shaped article. This method makes possible adjustment of wall thickness, and overcomes a disadvantage of the conventional vacuum method in that the bottom thickness of the cup is extremely thinned. However, when a crystalline thermoplastic resin sheet such as polypropylene sheet is used, accurate adjustment of the plug configuration becomes critical. It then is necessary to determine the optimum plug configuration and finely tailor the plug shape for each thermoformed article. U.S. Pat. No. 4,176,154 (Miki et al., 1979) discloses a method for producing a cup-shaped article which uses a concave forming mold and a recessed ancillary mold in mutual opposition. The ancillary mold includes a vertically movable molding assist. By introducing a pressured fluid into the forming mold, a preheated thermoplastic sheet interposed between the forming and ancillary molds is expanded into the ancillary mold while the molding assist is moving and in contact with the sheet. When the molding assist reaches a predetermined position, a pressured fluid introduced into the ancillary mold presses the sheet against the interior surface of the forming mold, thereby forming the desired shape. The method is applicable to deep-draw forming of cups having a depth-to-opening diameter ratio greater than 0.2.
Heretofore, no package has been provided which meets the specific requirements of addition cured dental impression materials. What is needed is a dual-compartment, air-tight sealed package which can be conveniently thermoformed, which will not be susceptible to leakage between compartments even after a long storage period, and which allows convenient dispensing of the base and catalyst portions.